The invention relates in general to a system for communication between two (or more) active functional units, for example, microprocessors or microcomputers. These units are interconnected by means of a data bus line having a data path width of, for example, 8 bits, and furthermore by a number of control-lines. In the case of only two active functional units, the data bus line acts as a single data link. On the other hand, the data bus line, and also the control lines, may be connected to a group of several (more than two) active functional units. A first active functional unit in this group then acts, for example, as a data source (talker), while the other functional units of this group together act as data operating in parallel destinations (listeners). The number of control lines then at least equals three. Thus, all these other active functional units together, however, can be considered to be only a single unit: viewed from the first active functional unit, the communication resembles an interaction between only two active functional units. The invention in particular concerns a device which includes at least two active functional units for the asynchronous transporting of digital data between said functional units by means of an interconnecting bidirectional data bus line together with at least two unidirectional control lines for carrying control signals for controlling data transmission, that is to say
a. a request signal in a first direction from a first active functional unit to a second active functional unit; PA1 b. an acknowledge signal in the opposite second direction from the second active functional unit to the first active functional unit;
the first active functional unit comprising a first circuit for instantaneously supplying, together with the generating of said request signal, data to be transported together in the first direction via the data bus line, the second active functional unit comprising a receiver which is connected to the data bus line. A system of this kind is known from the article by K. L. Thurber et al., A systematic aproach to the design of digital bussing structures, Proceedings AFIPS conf. Fall. 1972, pages 719-740, notably page 727, right column, FIG. 17 and the associated text. A request signal of this kind (data ready) is produced by a signal variation, for example, by a transition from a binary "1" to a binary"0" or vice versa. The same is applicable to the acknowledge signal (data accept). The communication system described provides data transport in only one direction.